By increasing the temperature of the iron sphere, its volume will increase (due to the material of which it is composed), this is a phenomenon known as thermal dilation. However, the mass of the sphere will remain the same.
On the other hand, density [tex]D[/tex] is a characteristic property of substances and materials and is defined as the relationship between the mass [tex]m[/tex] and volume [tex]V[/tex] of a specific substance or material, as shown below:
[tex]D=\frac{m}{V}[/tex]
This means density is inversely proportional to volume. Therefore, increasing the temperature of the iron sphere, its volume will be increased and its density will be decreased.
